1. Field of the Invention
This invention relates to flowmeters and more particularly, to flowmeters utilizing a variable area.
2. Background of the Invention
This invention relates to flowmeters of the type known as a variable area flowmeter. This type of flowmeter provides a weighted member movably disposed across an orifice such that the position of the weighted member determines the orifice area. The weighted member provides an essentially constant fluid head against the fluid entering the system so that the displacement of the weighted member is essentially a linear relation with the rate of volumetric flow of the fluid.
The principal advantage of a variable area flowmeter is that, at low cost, it provides a wide range of capacity with low system resistances and is essentially linear. One well known and popular form of variable area flowmeter, often called a rotameter, utilizes a weight moving vertically within a tapered tube, usually transparent, whose area increases upwardly. Among the disadvantages of this system is the inability to see the float and to read the flow when hidden by dark fluids in larger diameters toward the top of the tube. Rotameters are also subject to instability in the transition zone between laminar and turbulent flow and in many cases, viscosity influences the float response within the meter. These factors often limit accurate low end reading of rotameters to 8-12 percent of the total capacity. Certain desirable methods of applying a transducer for readout and control are limited by the geometry of a rotameter and for large flow rates, rotameters are large and costly. Finally, rotameters often experience severe float pulsation particularly with low density gas media.
Another proven variable area flowmeter is described in my prior U.S. Pat. No. 3,691,834. This invention overcomes many of the disadvantages of the rotameter. The U.S. Pat. No. 3,691,834 invention utilizes a snorkel for liquid media. The snorkel device adds cost, and requires a built-in minimum meter pressure drop to function. The snorkel, under some circumstances, may introduce an exponential flow factor which particularly limits wide range low capacity meter designs. In addition, the "thru slot" orifice configuration is difficult to construct in widths narrow enough to provide low capacity meters. In actual practice with metal core tubes and floats, full range capacities below about 1.2 gallons per minute for liquids and 7.0 standard cubic feet per minute for gases have been demonstrated impractical within competitive costs. Extreme float pulsation with low density gas media have been observed with the design, thus limiting the commercial application of this design.
It is a principal objective of this invention to provide a variable area flowmeter utilizing a float within and extending from a vertically oriented cylindrical within an orificed core tube which overcome deficiencies in the prior art.
Another object of this invention is to provide a variable area flowmeter utilizing tapered slot means and slots of various geometries producible without sophisticated machinery to allow full range capabilities in terms of flow rate.
Another object of this invention is to provide a variable area flowmeter wherein an effective pulsation damping means is provided therein without the cost and complications of a pitot or snorkel as found in my prior patent, U.S. Pat. No. 3,691,834.
Another object of this invention is to provide a variable area flowmeter which also eliminates unwanted flow components and the built-in pressure drop requirements inherent to the pitot or snorkel tube.
Another object of this invention is to provide a variable area flowmeter which generates signals for remote readout flow control and the like without sacrifice of inherent visual readout at the meter.
Another object of this invention is to provide a variable area flowmeter which is linear for an extremely wide variation in flow rates and density of fluid materials.
Another object of this invention is to provide a variable area flowmeter with means to provide departure from linearity when desired over full or upper range in either increasing or decreasing increments of displacement per unit of flow rate increase.
Another object of this invention is to provide a variable area flowmeter with a demonstrated accurate flow rate reading to one percent (1%) of full capacity.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner of modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.